Antenna impedance matching is a well-known aspect of RF design. Impedance matching networks are used in a variety of different communications devices for matching the radio portion to one or more antennas. Matching networks operate to minimize insertion loss and provide high receiver performance. Typically, the matching network of a communications device, such as a mobile phone, is included in the RF front-end module of the radio circuit included in the device. The RF front-end module may be defined as the circuitry located between an antenna port and a transceiver of the device.
The emergence of multi-band, multi-mode communications devices has introduced new challenges to the design of the RF front-end module and the matching networks included therein. As the number of frequency bands and radio access technologies (RATs) (also referred to in the art as communication standards) accommodated by a communications device increases, so does the complexity and cost of the RF front-end module within the device. Competing with the increasing demands on the radio portion of the device is the constant push for miniaturization of communications devices to satisfy the convenience and desires of consumers.
For example, mobile phones covering triple-band WCDMA (Wideband Code Division Multiple Access) and quad-band GSM (Global System for Mobile Communications) technologies with one antenna have been developed. However, the front-end module of such a multi-band, multi-mode device requires a large number of RF components to handle the numerous RF signal paths needed to cover all GSM and WCDMA frequency bands for both transmitting and receiving (e.g., one RF signal path for each frequency band covered by each RAT. To add further complexity, in order to provide maximum power transfer, the antenna impedance must be matched to each of the numerous RF signal paths.
FIGS. 5 and 6 illustrate conventional approaches to impedance matching in multi-band, multi-mode communications devices. FIG. 5 illustrates a conventional radio circuit that places an independent matching circuit on each RF signal path. The radio circuit of FIG. 5 provides perfect matching by providing an independent matching circuit for each signal path that is individually tailored to the specific frequency band, RAT, and TX/RX mode associated with the respective signal path. However, this increases the cost and complexity of the front-end module. The conventional radio circuit shown in FIG. 6 greatly reduces the number of RF components by including one common matching circuit. However, the common matching circuit of FIG. 6 provides fixed matching and thereby, compromises its performance across all frequency bands, RATs, and TX/RX modes. As a result, the radio circuit of FIG. 6 fails to provide the desired maximum power transfer.